In resent years, blood vessels have been employed as one of the subjects of biometric authentication. As a related art of such biometric authentication, an authentication apparatus has been proposed for extracting end points and a diverging point of a blood vessel on a captured image as feature points and generating data to be registered or data to be compared with registered data from the extracted feature points (see, for example, Patent Document 1). As compared with an authentication apparatus for setting image data itself as data to be registered, this authentication apparatus can markedly reduce memory occupancy of data to be stored.    Patent Document 1: Japanese Unexamined Patent Application Publication No. 2003-303178
However, since the end points and the diverging point are separate from one another on a blood vessel, they are unreliable data for making a determination whether a person is a registrant. Accordingly, even if feature points generated as data to be compared with registered data are the same as feature points generated as the registered data, the probability of determining that a person who is not a registrant is the registrant or a person who is the registrant is not the registrant by mistake due to external factors such as an image capturing environment and noise or internal factors such as (the difference between individuals in) the difficulty in capturing the image of blood vessels of living organisms is high. That is, the accuracy of authentication (the accuracy of determination whether a person is a registrant) is low.